Apparatus for generating a set of radio parameters, a transmitter and a receiver

ABSTRACT

A transmitter includes: a data modulation and channel coding unit configured to perform data modulation and channel coding for a data channel with a modulation level and a channel coding rate updated for each transmission time interval; a multiplexing unit configured to multiplex a control channel and the data channel for each transmission time interval; and an adjusting means configured to adjust a length of the transmission time interval. Increasing a unit of information transmission in the time direction and/or the frequency direction depending on communication conditions can reduce a frequency of inserting (allocating) the control channel, and can improve data transmission efficiency.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for generating a set ofradio parameters, a transmitter, and a receiver.

2. Description of the Related Art

In the mobile communication systems where video and/or data are mainlycommunicated, there is need of a much higher capability than in theconventional mobile communication systems (IMT-2000), and a highercapacity, a faster speed, and a broadband connection have to beachieved. In these systems, it is expected that they will be used undervarious communication environments such as indoor and outdoor areas.Under the outdoor areas, multiple cells (multi-cell) covering a widearea are provided for enabling fast packet transmission for afast-moving mobile station. Under the indoor areas, because radio wavesare attenuated more drastically, access points are provided withinbuildings without support of radio communications at outdoor basestations. From other viewpoints such as improved utilization efficiencyof communication resources, packet-based communications have beenemployed even in radio segments rather than conventional circuitswitched communications. In communications between a mobile station andan apparatus (upper node) located on the upper layer of a base station,particularly in downlink data transmission, not only a unicast schemebut also a multicast scheme and a broadcast scheme are employed. Forexample, see Non-Patent Reference 1 for an outlook of futurecommunication systems.

On the other hand, frequency selective fading under multipathenvironments has significant influence in wideband mobile communicationsystems. Hence, an OFDM (Orthogonal Frequency Division Multiplexing)system is promising as a next generation communication system. In theOFDM system, a single symbol is generated by attaching a guard intervalto an effective symbol including information to be transmitted, andmultiple symbols are transmitted during a predetermined transmissiontime interval (TTI). The guard interval consists of part of informationwithin the effective symbol. The guard interval may be also called acyclic prefix (CP) or overhead.

A receiver receives data on paths with various propagation delays.According to the OFDM system, if the amount of propagation delay fallswithin the period of the guard interval, inter-symbol interference canbe effectively reduced. Thus, a relatively large guard interval allowsdelay waves to be advantageously combined. This is advantageousparticularly in communications with an extremely large cell radius andin simultaneous transmission of the same information from differentcells to a mobile station in accordance with the multicast scheme.However, the guard interval includes only part of the effective symbol,and thus a larger period of the guard interval is not preferable fromthe viewpoint of information transmission efficiency. In some cases,satisfactory communication quality may be maintained under environmentswith relatively short propagation delay such as urban areas and indoorareas or environments available for the unicast scheme by setting arelatively short guard interval. Therefore, it is impossible todetermine a single type of guard interval optimized under variouscommunication environments. For this reason, it may be possible toprovide many sets of radio parameters for defining symbols includingguard intervals with various sizes to perform radio communications inthe adaptively selected optimal symbol format. However, signalprocessing corresponding to such various symbol formats leads to anextremely heavy workload, which is unfavorable for mobile stations witha relatively simple configuration. For a mobile station having no optionof an operating frequency (clock frequency), available signal processingis strictly limited, and thus the aforementioned problem may have aparticularly adverse effect on such a mobile station.

[Non-Patent Reference 1] Ohtsu, “Systems beyond IMT-2000”, ITU Journal,Vol. 33, No. 3, pp. 26-30, March 2000

SUMMARY OF THE INVENTION Problem(s) to be Solved by the Invention

The aforementioned transmission time interval (TTI) controls variousparameters for information transmission. For example, parameters such asa unit of packet transmission, a frequency of updating a data modulationscheme and a channel coding rate in the case of MCS (Modulation andCoding Scheme), a unit of error correction coding, a unit ofretransmission in the case of ARQ (Automatic Repeat reQuest), and a unitof packet scheduling are determined by the TTI. Because a controlchannel, which includes control information such as MCS information,retransmission information, and scheduling information, is used fordemodulating a data channel, the control channel has to be used alongwith the data channel during each TTI. On the other hand, a user cantransmit information during one or more TTIs, depending on the contentsof information to be transmitted. Accordingly, when multiple TTIs areused for data transmission, control channels for the respective TTIs aremultiplexed for transmission. However, when the same user transmits datacontinuously (see FIG. 1), the control channel may not be alwaysnecessary for each TTI, because it is not necessary to change radioparameters for each TTI. The situation where the control channel is usedfor transmission during each TTI is not preferable from the viewpoint ofdata transmission efficiency.

An OFDM mobile communication system is under discussion, where a widefrequency band is divided into multiple frequency blocks and a unit ofinformation transmission in the frequency direction is defined by thefrequency block. The frequency block is also referred to as a chunk (ora resource block), and a single frequency block includes one or moresubcarriers. A user can transmit information with one or more frequencyblocks. When multiple frequency blocks are used for data transmission,multiple control channels for the respective frequency blocks aremultiplexed for transmission, because the data channel is used fortransmission for each frequency block. These control channels mayinclude information about frequency block allocation in addition to theaforementioned MCS information and so on. Again, when the same usertransmits data with multiple frequency blocks (see FIG. 2), the controlchannel may not be always necessary for each frequency block. Thesituation where the control channel is used for transmission for eachfrequency block is not preferable from the viewpoint of datatransmission efficiency.

The present invention addresses at least one of the aforementionedproblems. It is a general object of the present invention to provide atransmitter, a receiver, and an apparatus for generating a radioparameter, which can improve information transmission efficiency in anOFDM mobile transmission system.

Means for Solving the Problem

According to one aspect of the present invention, there is provided anOFDM transmitter, which includes:

a data modulation and channel coding unit configured to perform datamodulation and channel coding for a data channel with a modulation leveland a channel coding rate updated for each transmission time interval;

a multiplexing unit configured to multiplex a control channel and thedata channel for each transmission time interval; and

an adjusting means configured to adjust a length of the transmissiontime interval.

Effect of the Invention

According to an embodiment of the present invention, it is possible toimprove information transmission efficiency in an OFDM mobilecommunication system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a case where control channels and data channels are usedfor transmission.

FIG. 2 shows a case where control channels and data channels are usedfor transmission.

FIG. 3 shows a (first) block diagram for illustrating a transmitter inaccordance with one embodiment of the present invention.

FIG. 4 shows a (second) block diagram for illustrating a transmitter inaccordance with one embodiment of the present invention.

FIG. 5 shows a block diagram for illustrating a receiver in accordancewith one embodiment of the present invention.

FIG. 6 shows a relationship between two types of TTI (a long TTI and ashort TTI) and a frame.

FIG. 7 shows a case where control channels and data channels are usedfor transmission.

FIG. 8 shows a case where control channels and data channels are usedfor transmission.

FIG. 9 shows symbol formats respectively defined by sets of symbolparameters derived in accordance with one embodiment of the presentinvention.

FIG. 10 shows various sets of symbol parameters derived in accordancewith one embodiment of the present invention.

FIG. 11 shows symbol formats respectively defined by sets of symbolparameters derived in accordance with one embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Description of Notations

-   -   302-1 to 302-N_(D): data channel processing unit    -   304: control channel processing unit    -   306: multiplexing unit    -   308: Inverse Fast Fourier Transform unit    -   310: guard interval insertion unit    -   312: digital to analog (D/A) conversion unit    -   320: symbol parameter adjusting unit    -   321: TTI adjusting unit    -   322: turbo coder    -   324: data modulator    -   326: interleaver    -   328: serial to parallel (S/P) conversion unit    -   342: convolution coder    -   344: QPSK modulator    -   346: interleaver    -   348: serial to parallel (S/P) conversion unit    -   402: orthogonal modulator    -   404: local oscillator    -   406: bandpass filter    -   408: mixer    -   410: local oscillator    -   412: bandpass filter    -   414: power amplifier    -   502: antenna    -   504: low noise amplifier    -   506: mixer    -   508: local oscillator    -   510: bandpass filter    -   512: automatic gain control unit    -   514: orthogonal detector    -   516: local oscillator    -   518: analog to digital conversion unit    -   520: symbol timing detection unit    -   522: guard interval removal unit    -   524: Fast Fourier Transform unit    -   526: demultiplexer    -   528: channel estimation unit    -   530: channel compensation unit    -   532: parallel to serial (P/S) conversion unit    -   534: channel compensation unit    -   536: deinterleaver    -   538: turbo decoder    -   540: Viterbi decoder    -   542: symbol parameter adjusting unit    -   544: TTI adjusting unit

BEST MODE OF CARRYING OUT THE INVENTION

According to one aspect of the present invention, a transmission timeinterval (TTI) is adjusted depending on communication conditions. Acontrol channel is multiplexed with a data channel for each TTI. Thecontrol channel may be multiplexed into part of subcarriers. Increasinga unit of information transmission in the time direction and/or thefrequency direction depending on communication conditions can reduce afrequency of inserting (allocating) the control channel, and can improvedata transmission efficiency.

The control channel may include information about a modulation level anda channel coding rate. The transmitter may store two or more sets ofparameters, each of which defines a symbol including a guard intervalwith a different period and an effective symbol with the same period.The transmitter can determine a symbol format-depending on communicationconditions without delay.

According to one aspect of the present invention, there is provided anapparatus for generating a set of radio parameters used for an OFDMmobile communication system which transmits and receives multiplesymbols for each transmission time interval, each of the multiplesymbols including a guard interval and an effective symbol. Theapparatus includes a first deriving unit configured to derive a secondset of symbol parameters, so that a period of an effective symboldefined by a first set of symbol parameters is equal to a period of aneffective symbol defined by the second set of symbol parameters, and aperiod of a guard interval defined by the first set of symbol parametersis different from a period of a guard interval defined by the second setof symbol parameters. The apparatus also includes a second deriving unitconfigured to derive a third set of symbol parameters, so that a shareof a guard interval in a symbol defined by the first set of symbolparameters is equal to a share of a guard interval in a symbol definedby the third set of symbol parameters, and a length of the symboldefined by the first set of symbol parameters is different from a lengthof the symbol defined by the third set of symbol parameters. A length ofthe transmission time interval, a length of the symbol, or both a lengthof the transmission time interval and a length of the symbol is adjustedso that an integral number of symbols are transmitted during a singletransmission time interval. The apparatus can effectively derive a setof radio parameters which has a desired number of subcarriers to beused, a desired loss rate (a share of a guard interval in a symbol), anda desired number of symbols within one or more TTIs. For example,assuming that periods of effective symbols are mutually equal (i.e.subcarrier intervals are mutually equal), any radio communication devicecan always use the same signal processing for OFDM modulation anddemodulation (Inverse Fast Fourier Transform and Fast Fourier Transform)even if any set of symbol parameters is used. Also assuming that theloss rate is kept constant, data transmission efficiency can be alsokept constant even if any set of symbol parameters is used.

According to one aspect of the present invention, a set of symbolparameters is derived so that the subcarrier interval and the loss ratehave desired values. For example, the number of subcarriers defined by acertain set of symbol parameters may be determined to be an integralmultiple of the number of subcarriers defined by another set of symbolparameters. As a result, a set of symbol parameters with a significantlydifferent period of the guard interval can be derived while controllingthe subcarrier interval and the loss rate. When a non-integral number ofsymbols, which are derived while controlling the loss rate, are includedin a single transmission time interval, the number of symbols for eachtransmission time interval can be adjusted to be an integer by extendingthe transmission time interval. Such an adjustment is preferable fromthe viewpoint of simplified signal processing.

First Embodiment

Although a system employing OFDM (Orthogonal Frequency DivisionMultiplexing) for downlink communications is described in the followingembodiment, the present invention is also applicable to othermulti-carrier systems.

FIG. 3 shows a (first) block diagram for illustrating a transmitter inaccordance with one embodiment of the present invention. Although thistransmitter is typically included in a base station, the sametransmitter may be also included in a mobile station. A base stationincludes N_(D) data channel processing units 302-1 to 302-N_(D), acontrol channel processing unit 304, a multiplexing unit (MUX) 306, anInverse Fast Fourier Transform (IFFT) unit 308, a guard intervalinsertion unit 310, a digital to analog (D/A) conversion unit 312, asymbol parameter adjusting unit 320, and a TTI adjusting unit 321. TheN_(D) data channel processing units 302-1 to 302-N_(D) mutually have thesame configuration and function, and the data channel processing unit302-1 is representatively described hereinafter. The data channelprocessing unit 302-1 includes a turbo coder 322, a data modulator 324,an interleaver 326, and a serial to parallel (S/P) conversion unit 328.The control channel processing unit 304 includes a convolution coder342, a QPSK modulator 344, an interleaver 346, and a serial to parallel(S/P) conversion unit 348.

The N_(D) data channel processing units 302-1 to 302-N_(D) performbaseband processing for transmitting traffic information data in theOFDM system. The turbo coder 322 performs encoding for enhancing errortolerance of the traffic information data. The data modulator 324modulates the traffic information data in accordance with a propermodulation scheme such as QPSK, 16QAM and 64QAM. In the case of adaptivemodulation and coding (AMC), this modulation scheme is modified ifneeded. The interleaver 326 sorts the traffic information data inaccordance with a predetermined pattern. The serial to parallel (S/P)conversion unit 328 converts a serial signal sequence (stream) intoparallel signal sequences. The number of parallel signal sequences maybe determined based on the number of subcarriers. The data channelprocessing units 302-1 to 302-N_(D) perform the aforementionedoperations for each transmission time interval supplied by the TTIadjusting unit 321.

The control channel processing unit 304 performs baseband processing fortransmitting control information data in OFDM system. The convolutioncoder 342 performs encoding for enhancing error tolerance of the controlinformation data. The QPSK modulator 344 modulates the controlinformation data in accordance with the QPSK modulation scheme. Anyother proper modulation scheme may be employed, however, the QPSKmodulation scheme with a lower number of modulation levels is employedin this embodiment due to the lesser amount of control information data.The interleaver 346 sorts the control information data in accordancewith a predetermined pattern. The serial to parallel (S/P) conversionunit 348 converts a serial signal sequence into parallel signalsequences. The number of parallel signal sequences may be determinedbased on the number of subcarriers.

The multiplexing unit (MUX) 306 multiplexes the processed (modulated,encoded, etc.) traffic information data and the processed controlinformation data. In this embodiment, a pilot channel (reference signal)may be input into the multiplexing unit 306 and multiplexed. In otherembodiments, a pilot channel may be input into the serial to parallelconversion unit 348 and multiplexed in the frequency direction, as shownby the dotted line in FIG. 3. The multiplexing may be any scheme of timemultiplexing, frequency multiplexing, or both time and frequencymultiplexing.

The Inverse Fast Fourier Transform unit 308 performs Inverse FastFourier Transform for an input signal, and then performs OFDMmodulation.

The guard interval insertion unit 310 generates a symbol in compliancewith the OFDM system by adding a guard interval to the modulated signal.As is well-known, the guard interval is generated by duplicating part ofthe head or tail of the symbol to be transmitted.

The digital to analog (D/A) conversion unit 312 converts a basebanddigital signal into an analog signal.

The symbol parameter adjusting unit 320 adjusts symbol parameters foruse in communications.

The symbol parameters (set of symbol parameters) include someinformation for defining the format of the OFDM symbols, and include aset of information items for defining values such as the period T_(GI)of the guard interval, the period of the effective symbol, the share ofthe guard interval in a single symbol, and the subcarrier interval Δf.It should be noted that the period of the effective symbol is equal tothe reciprocal of the subcarrier interval 1/Δf. The symbol parameteradjusting unit 320 determines a proper set of symbol parametersdepending on communication conditions or instructions from otherdevices. For example, the symbol parameter adjusting unit 320 mayselectively use a different set of symbol parameters based on whethercommunications are carried out in accordance with the multicast scheme.For example, a set of symbol parameters for defining the guard intervalwith a shorter period may be employed in the unicast scheme, whereas aset of symbol parameters for defining the guard interval with a longerperiod may be employed in the multicast scheme. The symbol parameteradjusting unit 320 may compute and derive a proper set of symbolparameters on a case-by-case basis. Alternatively, the symbol parameteradjusting unit 320 may store multiple sets of symbol parameters in amemory in advance and may select one of the sets of symbol parameters ifneeded. The manner of deriving the set of symbol parameters will bedescribed below.

The TTI adjusting unit 321 determines the length of the transmissiontime interval (TTI), and supplies the determined length of thetransmission time interval to each data channel processing unit 302-1 to302-N_(D), the multiplexing unit 306, and the symbol parameter adjustingunit 320. The length of the TTI may be determined based on informationdetermined by an application such as a traffic size, information aboutthe base station such as a frequency bandwidth, and/or information abouta service type such as multicasting, unicasting, and broadcasting. Thetransmitter may notify the receiver of the determined length of thetransmission time interval by means of some control signals. Forexample, the length of the transmission time interval may be determinedwhen a call is connected.

FIG. 4 shows a (second) block diagram for illustrating a transmitter inaccordance with one embodiment of the present invention. In FIG. 4, theportion (RF transmission unit) subsequent to the digital to analogconversion unit 312 in FIG. 3 is shown. The RF transmission unitincludes an orthogonal modulator 402, a local oscillator 404, a bandpassfilter 406, a mixer 408, a local oscillator 410, a bandpass filter 412,and a power amplifier 414.

The orthogonal modulator 402 generates an in-phase component (I) and aquadrature component (Q) of an intermediate frequency from an inputsignal. The bandpass filter 406 removes a frequency componentunnecessary for the intermediate frequency band. The mixer 408 uses thelocal oscillator 410 to convert (up-convert) the intermediate frequencysignal into a high frequency signal. The bandpass filter 412 removes anunnecessary frequency component. The power amplifier 414 amplifiessignal power for radio transmission from an antenna 416.

Traffic information data input into the data channel processing unit inFIG. 3 is encoded by the turbo coder 322, is modulated by the datamodulation unit 324, is sorted by the interleaver 326, and is madeparallel by the serial to parallel converter 328. Similarly, controlinformation data is encoded, modulated, interleaved, and made parallel.Data channels and control channels are multiplexed for each subcarrierand for each transmission time interval by the multiplexing unit 306,and are OFDM modulated by the Inverse Fast Fourier Transform unit 308.Then, a guard interval is added to the modulated signal for outputtingbaseband OFDM symbols. The baseband signal is converted into an analogsignal. Then, the converted signal is orthogonally modulated by theorthogonal modulator 402 in the RF processing unit in FIG. 4. Afterband-limiting, the modulated signal is properly amplified andtransmitted.

FIG. 5 shows a block diagram for illustrating a receiver in accordancewith one embodiment of the present invention. Although this receiver istypically included in a mobile station, it may be also included in abase station. The receiver includes an antenna 502, a low noiseamplifier 504, a mixer 506, a local oscillator 508, a bandpass filter510, an automatic gain control unit 512, an orthogonal detector 514, alocal oscillator 516, an analog to digital conversion unit 518, a symboltiming detection unit 520, a guard interval removal unit 522, a FastFourier Transform unit 524, a demultiplexer 526, a channel estimationunit 528, a channel compensation unit 530, a parallel to serial (P/S)conversion unit 532, a channel compensation unit 534, a deinterleaver536, a data demodulation unit 537, a turbo decoder 538, a Viterbidecoder 540, a symbol parameter adjusting unit 542, and a TTI adjustingunit 544.

The low noise amplifier 504 properly amplifies a signal received via theantenna 502. The amplified signal is converted (down-converted) into anintermediate frequency by the mixer 506 and the local oscillator 508.The bandpass filter 510 removes an unnecessary frequency component. Theautomatic gain control unit 512 controls the gain of the amplifier so asto properly maintain the signal level. The orthogonal detector 514 usesthe local oscillator 516 to perform orthogonal demodulation based on anin-phase component (I) and a quadrature component (Q) of the receivedsignal. The analog to digital conversion unit 518 converts an analogsignal into a digital signal.

The symbol timing detection unit 520 detects timing of symbols (symbolboundary) based on the digital signal.

The guard interval removal unit 522 removes a portion corresponding tothe guard interval from the received signal.

The Fast Fourier Transform unit 524 performs Fast Fourier Transform foran input signal, and then performs OFDM demodulation.

The demultiplexer 526 extracts pilot channels, control channels, anddata channels multiplexed into a received signal. This extraction isperformed corresponding to multiplexing at the transmitter (operationsin the multiplexing unit 306 in FIG. 3).

The channel estimation unit 528 uses the pilot channels to estimateconditions of the propagation path, and outputs a control signal foradjusting the amplitude and phase to compensate for the channelfluctuations. This control signal is output for each subcarrier.

The channel compensation unit 530 adjusts the amplitude and phase of thedata channels for each subcarrier based on information input from thechannel estimation unit 528.

The parallel to serial (P/S) conversion unit 532 converts parallelsignal sequences into a serial signal sequence.

The channel compensation unit 534 adjusts the amplitude and phase of thecontrol channels for each subcarrier based on information input from thechannel estimation unit 528.

The deinterleaver 536 sorts signals in accordance with a predeterminedpattern. The predetermined pattern corresponds to the inverse patternfor sorting in the interleaver (326 in FIG. 3) in the transmitter.

The data demodulation unit 537 performs demodulation for the receivedsignal for each transmission time interval, corresponding to themodulation scheme in the transmitter.

The turbo coder 538 and the Viterbi decoder 540 decode trafficinformation data and control information data, respectively.

The symbol parameter adjusting unit 542 determines symbol parameters foruse in communications as is the case with the symbol parameter adjustingunit 320 in FIG. 3. The symbol parameter adjusting unit 542 may computeand derive a proper set of symbol parameters on a case-by-case basis.Alternatively, the symbol parameter adjusting unit 542 may storemultiple sets of symbol parameters in a memory in advance and accessthem if needed. The manner of deriving the set of symbol parameters willbe described below.

The TTI adjusting unit 544 determines the length of the transmissiontime interval, and supplies the determined length of the transmissiontime interval to the demultiplexer 526, the deinterleaver 536, the datademodulation unit 537, the turbo decoder 538, and the symbol parameteradjusting unit 542. The transmitter may notify the receiver of thedetermined length of the transmission time interval by means of somecontrol signals. For example, the length of the transmission timeinterval may be determined when a call is connected.

A signal received via an antenna is converted into a digital signalafter amplification, frequency conversion, band-limiting, and orthogonaldemodulation in the RF reception unit. The Fast Fourier Transform unit524 performs an OFDM demodulation for a signal without a guard interval.The demodulated signal is demultiplexed into pilot channels, controlchannels, and data channels in the demultiplexer 526. The pilot channelsare input to the channel estimation unit 528, and a compensation signalfor compensating for channel fluctuations is output from the channelestimation unit 528 for each subcarrier. The data channels arecompensated for by means of the compensation signal for each subcarrierand are converted into a serial signal. The converted signal is sortedby the deinterleaver 526 in accordance with the inverse pattern forsorting in the interleaver and is decoded in the turbo decoder 538.Similarly, the control channels are also compensated for by means of thecompensation signal and are decoded in the Viterbi decoder 540.Afterward, signal processing is carried out with use of the decoded dataand control channels.

FIG. 6 shows data transmission in accordance with the presentembodiment. In this embodiment, the transmission time interval (TTI) isnot fixed, but two types of TTI (a long TTI and a short TTI) can be useddepending on communication conditions. It should be noted that thelength of the frame is kept constant in order to meet the requirementfor ensuring backward compatibility with existing communication systems.In the shown example, the long transmission time interval is twicelonger than the short transmission time interval. For example, thelength of the frame is equal to 10 ms, the length of the short TTI isequal to 0.5 ms, and the length of the long TTI is equal to 1.0 ms. Inthe case of the short TTI, a single frame includes 20 TTIs, whereas inthe case of the long TTI, a single frame includes only 10 TTIs. Althoughtwo types of TTI are provided in FIG. 6 for ease of explanation, moretypes of TTI may be provided.

As described above, the TTI controls various parameters for informationtransmission. For example, parameters such as a unit of packettransmission, a frequency of updating a data modulation scheme and achannel coding rate in the case of MCS, a unit of error correctioncoding, a unit of retransmission in the case of ARQ (Automatic RepeatreQuest), and a unit of packet scheduling are determined by the TTI.Because a control channel, which includes control information such asMCS information, retransmission information, and scheduling information,is used for demodulating a data channel, the control channel has to beused along with the data channel during each TTI. A longer TTI canreduce a frequency of inserting (allocating) the control channel, andcan improve information transmission efficiency (see FIG. 7).

This embodiment is also applicable to the case where a wide frequencyband is divided into multiple frequency blocks (or chunks) and a unit ofinformation transmission in the frequency direction is defined by thefrequency block. Specifically, when the same user transmits data usingmultiple frequency blocks, the control channel may not be used fortransmission for every chunk, but may be used for transmission only fora single chunk (see FIG. 8).

Flexibly changing a unit of information transmission in the timedirection and/or the frequency direction can prevent a frequency ofinserting (allocating) the control channel from unnecessarilyincreasing, and can improve information transmission efficiency.Adjusting the length of the TTI is advantageous particularly in the caseof a relatively narrow frequency band, because transmission efficiencyis directly related to transmission delay when an available frequencyband is narrow as shown in FIG. 7.

Second Embodiment

Next, a set of symbol parameters and deriving method thereof in thesymbol parameter adjusting units 320 (FIG. 3) and 542 (FIG. 5) aredescribed below. The set of symbol parameters defines the subcarrierinterval, the sampling frequency, the period of the effective symbol,the period of the guard interval, the number of symbols in a single TTI,and so on. It should be noted that all of the parameters cannot bedetermined independently. For example, the subcarrier interval and theperiod of the effective symbol have a reciprocal relationship with eachother. Also, the period of a single TTI is derived by multiplying theperiod of one symbol (total period of the guard interval and theeffective symbol) with the number of symbols. Three methods of derivinga second set of symbol parameters from a first set of symbol parametersare described below.

First, as shown in FIG. 9(A), assume that the first set of symbolparameters is determined as follows.

subcarrier interval=22.5 kHz

the total number of subcarriers=200

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=256 samples (44.4 μs)

period of guard interval=32 samples (5.5 μs)

period of one symbol=288 samples (guard interval+effective symbol)

loss rate=32/288=11.1%

the number of symbols in one TTI=10

period of one TTI=0.5 ms

period of one frame=10 ms

The loss rate means a share of the guard interval in one symbol. Theguard interval is a redundant portion from the viewpoint of improveddata transmission efficiency. The loss rate η, the period T_(GI) of theguard interval, and the period T_(eff) of the effective symbol have therelationship as follows;

η=T _(GI)/(T _(GI) +T _(eff))*100[%].

(1) A first method of deriving a set of symbol parameters decreases thenumber of symbols in a single TTI and increases the period of the guardinterval while keeping the subcarrier interval constant. For example, ifa first set of symbol parameters now includes 10 symbols in a singleTTI, the number of symbols is reduced to 9. Then, the periodcorresponding to the reduced one symbol (288 samples) is equally dividedinto 9 portions, each of which is assigned to the guard interval. As aresult, as shown in FIG. 9(B), while the period of the effective symbol(256 samples) is kept equal, the single TTI includes 9 symbols withlonger periods of the guard interval. A second set of symbol parametersderived in this manner has the parameter values as follows.

subcarrier interval=22.5 kHz

the total number of subcarriers=200

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=256 samples (44.4 μs)

period of guard interval=64 samples (11.1 μs)

period of one symbol=320 samples

loss rate=64/320=20%

the number of symbols in one TTI=9

period of one TTI=0.5 ms

period of one frame=10 ms

According to the first method, if the number of symbols in one TTI isreduced to 8, the second set of symbol parameters has the parametervalues as follow (FIG. 9(C)).

subcarrier interval=22.5 kHz

the total number of subcarriers=200

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=256 samples (44.4 μs)

period of guard interval=104 samples (18.1 μs)

period of one symbol=360 samples

loss rate=104/360=28.9%

the number of symbols in one TTI=8

period of one TTI=0.5 ms

period of one frame=10 ms

Subsequently through similar operations, it is possible to derive setsof symbol parameters with different numbers of symbols in a single TTI.In this case, the period of the effective symbol is always keptconstant, and thus the subcarrier interval can also be kept constant. Inother words, while the same subcarrier interval is defined in accordancewith any set of symbol parameters derived in this manner, the period ofthe guard interval and the number of symbols vary depending on the setof symbol parameters.

(2) A second method of deriving a set of symbol parameters changes thenumber of symbols in a single TTI while maintaining a constant lossrate. As understood from the definition of the loss rate, the share ofthe guard interval and the effective symbol has to be kept constant soas to fulfill the constant loss rate. For example, for the first set ofsymbol parameters, as shown in FIG. 9(D), the periods of the guardinterval and the effective symbol are doubled respectively, andaccordingly the number of symbols in one TTI can be reduced to 5symbols. In this case, the second set of symbol parameters has theparameter values as follows.

subcarrier interval=11.25 (=22.5/2) kHz

the total number of subcarriers=400 (=200*2)

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=512 (=256*2) samples (88.8 μs)

period of guard interval=64 (=32*2) samples (11.1 μs)

period of one symbol=576 samples

loss rate=64/576=11.1%

the number of symbols in one TTI=5

period of one TTI=0.5 ms

period of one frame=10 ms

In addition, for the first set of symbol parameters, as shown in FIG.9(E), the periods of the guard interval and the effective symbol arequadrupled respectively, and accordingly the number of symbols in oneTTI can be reduced to 2.5 symbols. In this case, the second set ofsymbol parameters has the parameter values as follows. In this case, itis desirable that the period of a single TTI be extended from 0.5 ms to1.0 ms, for example, so that an integral number of symbols are includedin the single TTI.

subcarrier interval=5.625 (=22.5/4) kHz

the total number of subcarriers=800 (=200*4)

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=1024 (=256*4) samples (177.8 μs)

period of guard interval=128 (=32*4) samples (22.2 μs)

period of one symbol=1152 samples

loss rate=128/1152=11.1%

the number of symbols in one TTI=2.5

period of one TTI=0.5 ms

period of one frame=10 ms

According to this method, the constant loss rate can be maintained, andthus it is possible to derive sets of symbol parameters with equal datatransmission efficiency. In the first method, as the number of symbolsin a single TTI decreases, the loss rate increases accordingly.

(3) A third method of deriving a set of symbol parameters is configuredas a combination of the first method and the second method. For example,the first method may be applied to a first set of symbol parameters toderive a second set of symbol parameters, and in turn the second methodmay be applied to the second set of symbol parameters to derive a thirdset of symbol parameters. Assume that applying the first method to thefirst set of symbol parameters has resulted in the second set of symbolparameters for defining a symbol format as shown in FIG. 9(B). Then, theloss rate is equal to 64/320=20% for the second set of symbolparameters. For the second set of symbol parameters, the number ofsymbols is modified while maintaining the constant loss rate. Forexample, if the periods of the guard interval and the effective symbolare duplicated respectively, the third set of symbol parameters has theparameter values as follows (FIG. 9(F)).

subcarrier interval=11.25 kHz

the total number of subcarriers=400

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=512 samples (88.8 μs)

period of guard interval=128 samples (22.2 μs)

period of one symbol=640 samples

loss rate=128/640=20%

the number of symbols in one TTI=4.5

period of one TTI=0.5 ms

period of one frame=10 ms

Also in this case, it is desirable that the period of a single TTI beextended to 1.0 ms, for example, so that an integral number of symbolsare included in the single TTI.

The third set of symbol parameters derived in this manner includes thesame loss rate (20%) as the set of symbol parameters shown in FIG. 9(B),and includes the same subcarrier interval (11.25 kHz) as the set ofsymbol parameters shown in FIG. 9(D). However, it should be noted thatthe period of the guard interval (128 samples) for the third set ofsymbol parameters is longer than any ones (64 samples) shown in FIGS.9(B) and 9(D). According to the third method, it is possible toefficiently derive a set of symbol parameters with a predeterminedrelationship between the subcarrier interval and the loss rate. Inaddition, because all of the sets of symbol parameters are prepared forthe same sampling frequency, it is not necessary to change clockfrequency for each of the sets of parameters.

FIG. 10 shows several exemplary sets of symbol parameters in case ofTTI=0.5 ms. Among 9 sets of symbol parameters, 8 sets of symbolparameters can be derived by applying the first method and/or the secondmethod to the first set of symbol parameters. According to thisembodiment, it is possible to systematically and efficiently derive setsof symbol parameters with predetermined relationships between thesubcarrier interval and the loss rate. In this embodiment, new sets ofsymbol parameters have been derived in such a manner that the subcarrierinterval and the number of symbols can be reduced from those of thereference set of symbol parameters. In other embodiments, however, suchnew sets of symbol parameters may be derived in such a manner that thesubcarrier interval and the number of symbols can be increased fromthose of the reference set of symbol parameters.

Third Embodiment

According to the first embodiment, the length of the transmission timeinterval (TTI) is adjusted. According to the second embodiment, thelength of the guard interval and/or the effective symbol is modified.These embodiments may be used independently or used in combination asdescribed below.

First, as shown in FIG. 11(A), assume that the first set of symbolparameters is determined as follows. These parameter values are the sameas those in FIG. 9(A), except that the period of one TTI is extendedfrom 0.5 ms to 1.0 ms.

subcarrier interval=22.5 kHz

the total number of subcarriers=200

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=256 samples (44.4 μs)

period of guard interval=32 samples (5.5

period of one symbol=288 samples (guard interval+effective symbol)

loss rate=32/288=11.1%

the number of symbols in one TTI=20

period of one TTI=1.0 ms

period of one frame=10 ms

(1) A first method of deriving a set of symbol parameters extends theperiod of the TTI, decreases the number of symbols in the single TTI,and increases the period of the guard interval while keeping thesubcarrier interval constant. For example, if a first set of symbolparameters now includes 20 symbols in a single TTI, the number ofsymbols is reduced to 19. Then, the period corresponding to the reducedone symbol (288 samples) is equally divided into 19 portions, each ofwhich is assigned to the guard interval. As a result, as shown in FIG.11(B), while the period of the effective symbol (256 samples) is keptequal, the single TTI includes 19 symbols with longer periods of theguard interval. A second set of symbol parameters derived in this mannerhas the parameter values as follows.

subcarrier interval=22.5 kHz

the total number of subcarriers=200

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=256 samples (44.4 μs)

period of guard interval=47.16 samples (8.187 μs)

period of one symbol=303 samples

loss rate=47/303=15.5%

the number of symbols in one TTI=19

period of one TTI=1.0 ms

period of one frame=10 ms

According to the first method, if the number of symbols in one TTI isreduced to 18, the second set of symbol parameters has the parametervalues as follow (FIG. 11(C)).

subcarrier interval=22.5 kHz

the total number of subcarriers=200

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=256 samples (44.4 μs)

period of guard interval=64 samples (11.1 μs)

period of one symbol=320 samples

loss rate=64/320=20.0%

the number of symbols in one TTI=18

period of one TTI=1.0 ms

period of one frame=10 ms

Subsequently through similar operations, it is possible to derive setsof symbol parameters with different numbers of symbols in a single TTI.In this case, the period of the effective symbol is always keptconstant, and thus the subcarrier interval can also be kept constant. Inother words, while the same subcarrier interval is defined in accordancewith any set of symbol parameters derived in this manner, the period ofthe guard interval and the number of symbols vary depending on the setof symbol parameters. In the examples shown in FIGS. 9(B), 9(C), 11(B),and 11(C), the number of symbols in one TTI is reduced by one symbol ortwo symbols, and the period corresponding to the reduced symbol(s) isequally divided into the guard intervals in the remaining symbols. Inthe examples shown in FIG. 11, the transmission time interval isextended twice as the transmission time interval in the examples shownFIG. 9. As a result, while the loss rate is equal to 20% in the exampleshown in FIG. 9(B), the loss rate is reduced to 15.5% in the exampleshown in FIG. 11(C). Similarly, while the loss rate is equal to 28.9% inthe example shown in FIG. 9(C), the loss rate is reduced to 20.0% in theexample shown in FIG. 11(C). Extending the length of the TTI in thismanner can improve the loss rate, when the first method of the secondembodiment is used.

(2) A second method of deriving a set of symbol parameters extends theperiod of the TTI, and changes the number of symbols in the single TTIwhile maintaining a constant loss rate. As understood from thedefinition of the loss rate, the share of the guard interval and theeffective symbol has to be kept constant so as to fulfill the constantloss rate. For example, for the first set of symbol parameters, as shownin FIG. 11(D), the periods of the guard interval and the effectivesymbol are doubled respectively, and accordingly the number of symbolsin one TTI can be reduced to 10 symbols. In this case, the second set ofsymbol parameters has the parameter values as follows.

subcarrier interval=11.25 (=22.5/2) kHz

the total number of subcarriers=400 (=200*2)

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=512 (=256*2) samples (88.8 μs)

period of guard interval=64 (=32*2) samples (11.1 μs)

period of one symbol=576 samples

loss rate=64/576=11.1%

the number of symbols in one TTI=10

period of one TTI=1.0 ms

period of one frame=10 ms

In addition, for the first set of symbol parameters, as shown in FIG.11(E), the periods of the guard interval and the effective symbol arequadrupled respectively, and accordingly the number of symbols in oneTTI can be reduced to 5 symbols. In this case, the second set of symbolparameters has the parameter values as follows.

subcarrier interval=5.625 (=22.5/4) kHz

the total number of subcarriers=800 (=200*4)

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=1024 (=256*4) samples (177.8 μs)

period of guard interval=128 (=32*4) samples (22.2 μs)

period of one symbol=1152 samples

loss rate=128/1152=11.1%

the number of symbols in one TTI=5

period of one TTI=1.0 ms

period of one frame=10 ms

According to this method, the constant loss rate can be maintained, andthus it is possible to derive sets of symbol parameters with equal datatransmission efficiency. In the first method, as the number of symbolsin a single TTI decreases, the loss rate increases accordingly. Althoughthe number of symbols in one TTI is equal to 2.5 symbols in the exampleshown in FIG. 9(E), the number of symbols is equal to 5 symbols in FIG.11(E). In this manner, when a non-integral number of symbols areincluded in a single TTI with use of the method of the secondembodiment, extending the length of the TTI allows the number of symbolsin the single TTI to be adjusted to be an integer.

(3) A third method of deriving a set of symbol parameters is configuredas a combination of the first method and the second method whileextending the period of the TTI. For example, the first method may beapplied to a first set of symbol parameters to derive a second set ofsymbol parameters, and in turn the second method may be applied to thesecond set of symbol parameters to derive a third set of symbolparameters. Assume that applying the first method to the first set ofsymbol parameters has resulted in the second set of symbol parametersfor defining a symbol format as shown in FIG. 11(B). Then, the loss rateis equal to 15.5% for the second set of symbol parameters. For thesecond set of symbol parameters, the number of symbols is modified whilemaintaining the constant loss rate. For example, if the periods of theguard interval and the effective symbol are duplicated respectively, thethird set of symbol parameters has the parameter values as follows (FIG.11(F)).

subcarrier interval=11.25 kHz

the total number of subcarriers=400

sampling frequency=5.76 MHz=3/2*3.84 MHz

period of effective symbol=512 samples (88.8 μs)

period of guard interval=94.3 samples (16.37 μs)

period of one symbol=606.3 samples

loss rate=94.3/606.3=15.5%

the number of symbols in one TTI=9

period of one TTI=1.0 ms

period of one frame=10 ms

The third set of symbol parameters derived in this manner includes thesame loss rate (15.5%) as the set of symbol parameters shown in FIG.11(B), and includes the same subcarrier interval (11.25 kHz) as the setof symbol parameters shown in FIG. 11(D). However, it should be notedthat the period of the guard interval (94.3 samples) for the third setof symbol parameters is longer than any ones shown in FIGS. 11(B) and11(D). According to the third method, it is possible to efficientlyderive a set of symbol parameters with a predetermined relationshipbetween the subcarrier interval and the loss rate. In addition, becauseall of the sets of symbol parameters are prepared for the same samplingfrequency, it is not necessary to change clock frequency for each of thesets of parameters. Moreover, the number of symbols included in thesingle TTI can be adjusted to be an integer.

Although the preferred embodiments of the present invention have beendescribed above, the present invention is not limited to them, andvarious modifications and variations can be made within the scope andsprit of the present invention. For ease of explanation, the presentinvention has been described with the use of some discrete embodiments.However, such separation of the embodiments is not essential to thepresent invention, and one or more embodiments may be used if needed.

This international patent application is based on Japanese PriorityApplication No. 2005-174396 filed on Jun. 14, 2005, the entire contentsof which are hereby incorporated by reference.

1. A transmitter used in an OFDM (Orthogonal Frequency DivisionMultiplexing) mobile communication system, comprising: a data modulationand channel coding unit configured to perform data modulation andchannel coding for a data channel with a modulation level and a channelcoding rate updated for each transmission time interval; a multiplexingunit configured to multiplex a control channel and the data channel foreach transmission time interval; and an adjusting means configured toadjust a length of the transmission time interval.
 2. The transmitter asclaimed in claim 1, wherein: the control channel is multiplexed intopart of subcarriers.
 3. The transmitter as claimed in claim 1, wherein:the control channel at least includes information about the modulationlevel and the channel coding rate.
 4. The transmitter as claimed inclaim 1, further comprising: a transmission unit configured to transmitmultiple symbols for each transmission time interval, each of themultiple symbols including a guard interval and an effective symbol; anda storing unit configured to store two or more sets of parameters, eachof the two ore more sets of parameters defining a symbol including aguard interval with a different period and an effective symbol with thesame period.
 5. A receiver used in an OFDM (Orthogonal FrequencyDivision Multiplexing) mobile communication system, comprising: ademultiplexing unit configured to extract a control channel and a datachannel for each transmission time interval; a data demodulation andchannel decoding unit configured to perform data demodulation andchannel decoding for the data channel with a modulation level and achannel coding rate updated for each transmission time interval; and anadjusting means configured to adjust a length of the transmission timeinterval.
 6. The receiver as claimed in claim 5, wherein: the controlchannel at least includes information about the modulation level and thechannel coding rate.
 7. The receiver as claimed in claim 5, furthercomprising: a receiving unit configured to receive multiple symbols foreach transmission time interval, each of the multiple symbols includinga guard interval and an effective symbol; and a storing unit configuredto store two or more sets of parameters, each of the two or more sets ofparameters defining a symbol including a guard interval with a differentperiod and an effective symbol with the same period.
 8. An apparatus forgenerating a set of radio parameters used for an OFDM (OrthogonalFrequency Division Multiplexing) mobile communication system whichtransmits and receives multiple symbols for each transmission timeinterval, each of the multiple symbols including a guard interval and aneffective symbol, comprising: a first deriving unit configured to derivea set of second symbol parameters, so that a period of an effectivesymbol defined by a first set of symbol parameters is equal to a periodof an effective symbol defined by the second set of symbol parameters,and a period of a guard interval defined by the first set of symbolparameters is different from a period of a guard interval defined by thesecond set of symbol parameters; and a second deriving unit configuredto derive a third set of symbol parameters, so that a share of a guardinterval in a symbol defined by the first set of symbol parameters isequal to a share of a guard interval in a symbol defined by the thirdset of symbol parameters, and a length of the symbol defined by thefirst set of symbol parameters is different from a length of the symboldefined by the third set of symbol parameters; wherein a length of thetransmission time interval, a length of the symbol, or both a length ofthe transmission time interval and a length of the symbol is adjusted sothat an integral number of symbols are transmitted during a singletransmission time interval.